Electronic oven with mode exciter and tuning probes

ABSTRACT

An electronic oven includes a heating cavity, a microwave antenna coupled to a source of microwave energy and disposed centrally of the bottom of said cavity for radiating thereinto microwave energy of a predetermined frequency for exciting a predetermined primary mode electromagnetic field in the cavity, a conductive member in the cavity adjacent to the top thereof and rotatably driven about the axis of the antenna for exciting secondary modes complementary to the primary mode at frequencies somewhat higher than the predetermined frequency, and two tuning members mounted at the top of the cavity adjacent to the path of the conductive members and symmetrically with respect thereto for coupling the highest frequency one of the secondary modes and reducing the frequency thereof without altering coupling of the primary mode.

United States Patent [191 Simon et a1,

m 3,823,295 [451 July 9,1974

1 ELECTRONIC OVEN WITH MODE EXCTTER AND TUNING PROBES [75] Inventors: Donald J. Simon; Louis H.

Fitzmayer, both of Louisville, Ky. [73] Assignee: Generall Electric @ompany,

Louisville, Ky. [22] Filed: Jan. 2, 1973 [21] Appl. No: 320,140

[52] US. E1. 219/1055 [51] 11m. 131. 1105b 9/06 [58] 1ie1tl of Search 219/1055 [56] References (Iited UNITED STATES PATENTS 3,281,567 10/1966 Meissner et al 219/1055 3,422,240 1/1969 Parker 219/1055 3,643,055 2/1972 Suzuki et a1. 219/1055 3,716,687

2/1973 Constable 219/1055 Primary Examiner'Bruce A. Reynolds Assistant Examiner- Hugh D. J aeger Attorney, Agent, or Firm-Prangley, Dithmar, Vogel, Sandler & Stotland I than the predetermined frequency, and two tuning members mounted at the top of the cavity adjacent to the path of the conductive members and symmetrically with respect thereto for coupling the highest frequency one of the secondary modes and reducing the frequency thereof without altering coupling of the primary modev ifila me 6 mu in figures l ELECTRONIC OVEN WI'll'II MODE EXCITE a IING FROBES The present invention is an improvement of the invention disclosed in our copending U. S. application, Ser. No. 317,206, filed Dec. 21, 1972, and entitled ELECTRONIC OVEN WITH MODE EXCITER, and assigned to the assignee of the present invention. More particularly, the present invention relates to a device for providing a substantially uniform timeaveraged field distribution in an electronic oven cavity to facilitate uniform heating of the material placed in he ven.

It is the general object of this invention to provide an electronic oven operating at a predetermined ultrahigh frequency and having primary and secondary electromagnetic field modes excited in the cavity with the secondary modes being at frequencies above the predetermined frequency, and including tuning means for coupling the secondary mode and lowering the frequency thereof toward the predetermined frequency, thereby to improve the operation of the electronic oven with light, shallow loads.

It is an important object of this invention to provide electronic heating apparatus comprising an enclosure including two opposed parallel walls and defining a heating cavity for receiving therein a body to be heated, an antenna disposed adjacent to one of the opposed walls and projecting into the cavity along an axis substantially perpendicular to the one wall, the antenna being adapted for coupling to an associated source of electromagnetic energy of a first predetermined ultrahigh frequency for transmitting the energy into the cavity to excite therein a predetermined primary electromagnetic field mode, a grounded conductive member sqsed n the svityas iaasstt tt s thet tttiespposed walls, drive means coupled to the conductive member for effecting rotation thereof about the axis of the antenna for exciting in the cavity a predetermined secondary mode complementary to the primary mode and at a second predetermined ultrahigh frequency, and tuning means mounted in the cavity for coupling the secondary electromagnetic field mode and changing the frequency thereof toward the first predetermined frequency substantially without effecting the coupling of the primary electromagnetic field mode, whereby there is established within the cavity a field distribution adapted to provide improved heating of the associated body.

In connection with the foregoing object, it is another object of this invention to provide electronic heating apparatus of the type set forth, wherein the conductive member in s st sn dssns stiv .sha end:

ing into the cavity with the longitudinal axis thereof disposed substantially parallel to the electric field component of the primary mode, and a generally L-shaped conductive member connected to the shaft and having two interconnected leg portions disposed in the cavity in a plane substantially normal to the axis of the shaft, and two tuning members mounting in the cavity adjacent to the predetermined path and arranged symmetrically with respect to the axis thereof.

Further features of the invention pertain to the particular arrangement of the parts of the electronic heating apparatus whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the w easgsq fis on, a e nsonnest t the accompanying drawings, in which:

FIG. I is a side elevational view in partial section of an electric range incorporating therein an electronic heating apparatus constructed in accordance with and embodying the features of the present invention;

FIG. 2 is an enlarged fragmentary bottom-plan view f. e ovsahrgil it, a a 1 99 grate n t n probes, taken along the line 2-2 in FIG. I; I

FIG. 3 is a fragmentary front elevational view of the oven cavity showing the arrangement therein of the mode exciter and tuning probes of the present invention;

FIG. 4 is a view similar to FIG. 2, showing an alternative embodiment of mode stirrer for use with the present invention;

' FIG. 5 isa top-plan diagrammatic representation of the oven cavity of the present invention showing the area of strong resultant electric field of the TE and TE ll modes when the mode exciter is in the posi- QFLIUEEEEL QLQEQW FIG. 6 is a bottom-plan diagrammatic view similar to FIG. 5 and showing the region of strong resultant electric when the mode exciter is in the position illustrated in FIG. 5.

Referring now more particularly to FIGS. l and 2 of the drawings, there is illustratedan electric range, generally designated by the numeral 50. The detailed construction of the electric range is disclosed in the copending US. application Ser. No. 256,093 of RO- LAND V. FOWLER et aL, filed May 23, 1972, entitled MULTIPLE POSITION DOOR LATCH MECHA- NISM, and assigned to the assignee of the present invention. Accordingly, only so much of the structure of the range 50 will herein be described as is necessary for an understanding of the present invention.

The range 50 is generally box-like in shape and includes a top wall 51, a bottom wall 52, an upstanding regriwallfl, a front wall 55, and a pair of opposedup; standing side walls 54. Mounted on the top wall 51 of the range 5t) is a plurality of standard electrical resistance heating units, these units and the other heating apparatus of the range 50 being controlled by a set of controls carried by a control panel 56 mounted on the top wall 51 at the rear end thereof. The front wall has a relatively large rectangular upper opening 58 and a relative small rectangular lower opening 59 therein for providing access to the interior of the range 50. Connected to the front wall 55 and extending inwardly therefrom at the upper and lower edges of the opening 58 are two angle mounting flanges 63 and 64 which cooperate with similar flanges (not shown) at the sides of the opening 58 for defining a doorway.

A door 6t) is mounted on the front wall 55 for movement between an open position (not shown) providing access to the interior of the range 56 and a closed position illustrated in FIG. I disposed in the doorway for closing the opening 58. In like manner, a door 62 is mounted on the front wall 55 adjacent to the opening 59 for movement between an open position (not shown) providing access to the interior of the range 50 and a closed position, illustrated in FIG. l, for closing the opening 59. Connected to the upper mounting flange 63 and extending rearwardly therefrom substantially normal to the front wall 55 is a rectangular partition 65 for dividing the interior of the range 50 into an upper machinery compartment 66 and a lower oven compartment 67. Mounted in the upper machinery compartment 66 upon the partition 65 is a latch assembly 68 for latching the front door 60 in the closed position thereof.

Mounted in the lower oven compartment 67 a slight distance below the partition 65 is a generally boxlike metallic oven enclosure, gnerally designated by the numeral 70, the oven enclosure being substantially in the shape of a rectangular parallelepiped and including a top wall 71, a bottom wall 72, an upstanding rear wall 73, and a pair of opposed upstanding side walls 74, the front end of the oven enclosure 70 being open at the front end thereof and communicating with the opening 58 of the front wall 55 of the range 50. The top and bottom walls 71 and 72 and the side walls 74 of the enclosure 70 are connected at the front edges thereof to the mounting flanges 63 and 64 for supporting and positioning the oven enclosure 70 in the compartment 67.

Preferably, the side walls 74 of the oven enclosure 70 are provided on the inner surfaces thereof with mounting means (not shown) for supporting a rack 75, the rack 75 comprising a plurality oflaterally spaced-apart parallel rods 77 extending parallel to the side wall 74 and interconnected at the front and rear ends thereof by end rods 78 disposed substantially parallel to the rear wall 73 (see FIGS. 3 and 4). Disposed within the oven enclosure .70 closely adjacent to the top wall 71 and substantially parallel thereto is a broil unit 79 secured to the top wall 71 by means of mounting clips 71a, the broil unit 79 preferably being a resistance treating element arranged in the serpentine configuration illustrated in FIG. 2.

The bottom wall 72 of the oven enclosure 70 is p 2, s flist nss A2 12 theh tt wall 52 of the ran g e S ITand cooperates therewith to define therebetween a lower machinery compartment 88, access to which is provided through the front opening 59. Mounted in the lower machinery compartment 88 on the bottom wall 52 is a component tray 81 having mounted thereon a magnetron generator 80 for generating electromagnetic energy of a predetermined ultrahigh frequency, preferably 915 MHz. The magnetron 80 is energized by a power supply unit 82 which is also mounted on the component tray 81. The magnetron 80 and the power supply unit 82 may be of the type disclosed in the copending U. S. Pat. application Ser. No. 181,144 of James E. Staats, filed Mar. 20, I962, entitled Control and Power Supply Systems for Magnetron Devices, and assigned to the assignee of the present Also mounted in the lower machinery compartment 88 is a blower 83 for directing a stream of cooling air overthe magnetron 80 and the power supply 82 for effecting cooling thereof in a well-known manner. Coupled to the RF output terminals the magnetron 80 is a waveguide 84, the upper end of which is received in a complementary opening disposed centrally of the bottom wall 72 of the oven enclosure 70 and is coupled to an antenna, generally designated by the numeral 85, for radiating the microwave energy to the heating cavity defined by the oven enclosure 70 and the closed front door 60. The antenna 85 preferably includes a cylindrical metal post 86 extending vertically upwardly into the oven cavity substantially perpendicular to the bottom wall 72 and coaxially connected at the upper end thereof to a circular slightly concave disk-like capacitive member 87. Preferably, the post 86 has an electrical length approximately equal to /8 of the wavelength A of the microwave energy generated by the magnetron 80, the total electrical length of the antenna being approximately equal to the M4.

Mounted in the upper machinery compartment 66 is an electric drive motor 90 having a grounded conductive output shaft extending vertically downwardly through a complementary opening disposed centrally in the top wall 71 of the oven enclosure 70. The output shaft 95 is preferably disposed substantially coaxially with the post 86 of the antenna 85 and extends a predetermined distance into the oven into the heating cavity. Preferably, the shaft 95 has an electrical length approximately equal to M8.

Connected to the shaft 95 at the bottom end thereof is a mode stirrer or exciter which is one of several types, but is preferably of an L-shaped member or a W- shaped member, generally designated respectively by the numerals and 110, the L-shaped exciter 100 being illustrated in FIGS. 1 and 2, and the W-shaped exciter 110 being illustrated in FIG. 4.

The mode exciter 100 is preferably integrally formed of a single piece of conductive material such as metal,

the mode exciter 100 including a relatively long leg I01 and a relatively short leg 105, the leg being disposed substantially normal to the leg 101. Preferably, the mode exciter 100, is formed of a relatively thin flat piece of metal having a width and thickness sufficient to provide appropriate mechanical strength and current-carrying capacity, the width however preferably being less than or equal to M8. In the preferred embodiment of the invention, the mode exciter 100 is disposed in a plane substantially parallel to the top wall 71 of the oven enclosure 70 and is connected at the free end of the leg 101 to the bottom end of the shaft 95 for rotation therewith by the drive motor 90. The leg 101 preferably has an electrical length approximately equal to 3 M8, while the short leg 105 preferably has an electrical length approximately equal to M4, whereby the total electrical length of the shaft {53nd the mode exciter 100 is approximately equal to 3 M4.

The length, width and height of the heating cavity defined by the oven enclosure 70 are all preferably greater than A. Thus, in operation, the dimensions of the heating cavity and the dimensions of the antenna 75 are such that when the microwave energy is radiated into the cavity by the antenna 75, the heating cavity acts as a cavity resonator and there is established therein the TB, mode at approximately 920 MHz, the electric field component of which is maximum at the middle of the heating cavity and is minimum at the front and rear ends thereof, with the direction of the field 106 being substantially parallel to the axis of the grounded shaft 95, all as is clearly explained in our aforementioned copending U. S. application, Ser. No.

As the mode exciter 100 is rotated through the electric field 110, the mode exciter 100 is itself excited by the electric field 110 and in turn excites secondary mqges n the. IIQEWSP'sWlFLMQKQBi when the short leg 105 of the mode exciter l00 is disposed in positions parallel to the rear wall 73, it excites in the slsa satins av y e EhL- ds rmx ly 930935 MHZ, the electric field component of which is maximum adjacent to the front and rear ends of the cavity and is minimum at the center thereof. Similarly, when the long leg 1101 of the mode exciter 1100 is disposed in positions substantially parallel to the back wall 73, it excites in the cavitythe TE mode at approximately 690 MHZ, the electric field component of this mode being maximum at the center of the heating cavity and minimum adjacent to the front and rear ends thereof.

Both the TB and the TE secondary modes are complementary to the primary TIE mode and cooperate therewith to equalize the electric field pattern in the heating cavity. More particularly, it will be appreciated that, as the secondary modes TE, and the TE are periodically excited as the mode exciter 100 is rotated in the heating cavity, the electric fields of the several modes add algebraically so that the resultant timeaveraged electric field distribution in the oven cavity will be equalized, thereby facilitating more even heating of food placed in the oven cavity to be cooked.

It will be observed that, as the long leg 101 of the mode exciter I rotates, the phase orientation of the TE mode excited thereby, with respect to the primary TE mode, is automatically continually changed to provide optimum equalization of the resultant electric field pattern. However, the TE mode excited by the short leg 1105 maintains the same phase orientation with respect to the primary mode TE as the mode exciter 1100 is rotated. Thus, there will be a distortion of the resultant field of the TE and TE modes. In order to eliminate this distortion in the resultant field of the superimposed TE and TE modes, it is necessary to effect a periodic phase reversal of the mode orientation of the electric field of the TE, mode with respect to the electric field of the TE g mode.

The mode exciter H0 is for effecting this phase reversal. The mode exciter H0 is generally W-shaped and comprises two identically constructed L-shaped sections, each of which is substantially identical to the mode exciter i100. More particularly, the mode exciter field, and in particular the TE mode, is closer to the frequency of the primary mode. Accordingly, in order to effect this narrowing of the difference between the frequencies of the primary and secondary modes of the electric field, there are provided in the present invention two tuning probes substantially identical in construction and each generally designated by the numeral 120. Each of the tuning probes 120 is preferably integrally formed of metal and includes a flat generally rectangular main body portion 1121 having integral therewith at one end thereof and extending substantially normal thereto an upright flange 1122. Integral with the upright flange 1l22 at the upper. end thereof and extending therefrom substantially normal thereto away from the direction of the main body portion 121 is a short rectangular mounting flange 123.

M0 includes a first long leg portion lllll being integral and in a direction opposite to the direction of the short leg portion llll5. Integral with the second long leg portion H2 at the other end thereof and extending therefrom substantially normal thereto in a direction opposite to the direction of the first long leg portion Jill is a second short leg portion. llllb. Preferably, the leg portions llllll, I12, I15 and llllb ofthe mode stirrer 1110 are all disposed in a common plane substantially parallel to the top wall '71 of the oven enclosure '70, with the mode exciter 200 being connected at a point M7 at the junction of the long leg portions lllll and M2 to the lower end of the shaft 95 for rotation therewith by the motor 90.

In operation, the modeexciter I110 acts in the same manner as two of the L-shaped mode exciters I00. More particularly, the short leg portions 115 and 116 excite the secondary TE mode when they are disposed substantially parallel to the front and rear walls of the oven cavity, while when the long leg portions Ill is fixedly aimed thereto as by screws or bolts or other suitable fasteners. In this configuration, the main body portion 121 is disposed in a plane substantially parallel to the top wall 711 and spaced therebelow a distance equal to the length of the upright flange I22, as is best shown in FIG. 3. Preferably, the tuning probes 120 are respectively disposed on opposite sides of the shaft 95, with the main body portions I211 extending inwardly toward each other with the longitudinal axes thereof disposed in a common vertical plane passing through the longitudinal axis of the shaft and above the plane of rotation of the mode exciter 1100. Preferably, the tuning probes are equidistantly spaced from the shaft 95 a distance approximately equal to the length of the long leg ll0l of the mode exciter 1100.

The length and position of the tuning probes 1120 are such that the tuning probes 1120 do not affect the tuning fllli l M. m d F 920 Ml i s Pll f l several MIL, while at the same time 0 coupling the TE mode at 960 MH and lowering the frequency thereof into the 890-940 MH band, thereby to improve the operation of the electronic oven at light and shallow loads. In a constructional model of the electronic oven, the oven enclosure 70 has a height of approximately l6 inches, a width of approximately 23 inches, and a depth from front to back of approximately l7- /a inches, each of the tuning probes I20 having an effective electrical length of approximately M4 and being spaced approximately 45 inches from the shaft 95, the tuning probes 120 being individually adjusted to tune the TE mode between 890 and 940 MH As the long leg lltlll of the mode exciter 1100 approaches the vicinity of one of the tuning probes I20, as illustrated in FIG. 5, it detunes that probe causing an unbalance of the system resulting in the other tuning probe I20 coupling more of the TB mode than would normally be coupled by the long leg 1011 of the mode exciter 100 by itself. When this happens, the resultant electric field pattern in the oven, which is a composite of the TE and TIE/ modes, becomes unbalanced, with the areas of strong resultant field being disposed at the upper right-hand portion and lower left-hand portion of the oven enclosure 70 as indicated in FIGS. and 6. When the mode exciter 100 approaches the other tuning probe 120 an opposite unbalance occurs in the resultant electric field pattern. It will be appreciated that if the tuning probes 1120 are properly located, the unbalance in the resultant electric field moves from side to side in the oven enclosure 70 as the mode exciter 100 rotates, whereby there is no net excitation of the TE mode.

It will, of course, be appreciated that a similar phenomenon occurs when the W-shaped mode exciter 110 is used in place of the mode exciter 100. More particularly, as the long legs ill and 112 of the mode exciter 110 approach one of the tuning probes 120, they detune that probe, it being understood that with the W- shaped mode exciter 110 each of the tuning probes 120 will be detuned twice during each revolution of the mode exciter 1110. However, the resulting unbalance in the resultant electric field pattern in the oven cavity will move alternately from side to side in the oven cavity as the mode exciter lltl rotates, just as was explained above with respect to the mode exciter 100,

whereby there will be no net excitation of the TE mode.

From the foregoing, it can be seen that there has been provided a novel arrangement of electronic heating apparatus which provides a substantially uniform time-averaged electromagnetic field distribution in the oven cavity, while at the same time minimizing the difference between the frequencies of the primary and secondary electric field modes, thereby to facilitate uniform heating of bodies in the oven cavity and to improve operation of the electronic oven at light, shallow loads.

More particularly, there has been provided in combination a mode exciter which is rotatably driven in the primary mode electric field to excite secondary mode electric fields at frequencies above the frequency of the primary mode, and novel tuning members positioned and dimensioned in the oven cavity for coupling at least one of the secondary modes and lowering the frequency thereof toward the frequency of the primary mode.

There has also been provided an electronic heating apparatus of the character described, wherein the tuning means comprises a pair of tuning members arranged symmetrically with respect to the mode exciter so as to equalize any unbalance of the resultant electric field in the oven cavity produced by interaction between the tuning means and the mode exciter, thereby to effect a lowering of the frequency of the secondary mode while effecting no net excitation thereof.

While there has been described what is at present qonsiq rsd t9 be the.,nre sr siemrb qim m f h ini vention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. Electronic heating apparatus comprising an enclosure including two opposed parallel walls and defining a heating cavity for receiving therein a body to be heated, an antenna disposed in said cavity adjacent to one of said opposed walls and having a longitudinal axis substantially perpendicular to said one wall, said antenna being adapted for coupling to an associated source of microwave electromagnetic energy for transmitting said energy into said cavity to excite therein a predetermined primary electromagnetic field mode at a first mode frequency, a grounded conductive member disposed in said cavity adjacent to the other of said opposed walls, drive means coupled to said conductive member for effecting rotation thereof about said axis of said antenna for exciting in said cavity a predetermined secondary electromagnetic field mode complementary to said primary mode and at a second mode frequency, and tuning means mounted in said cavity for coupling said secondary electromagnetic field mode and changing the mode frequency thereof toward said first mode frequency substantially without affecting the coupling of said primary electromagnetic field mode, whereby there is established within said cavity a field distribution adapted to provide improved heating of the associated body.

2. The electronic heating apparatus set forth in claim 1, wherein said second mode frequency is higher than said first mode frequency, said tuning means effecting lowering of the frequency of said secondary mode to a range below said second mode frequency and including said first mode frequency.

3. The electronic heating apparatus set forth in claim 1, wherein said first mode frequency is approximately 920 MH and said second mode frequency is approximately 960 MH said tuning means effecting reduction of the frequency of said secondary mode to a range of frequencies between 890 and 940 MH 4. Electronic heating apparatus comprising an enclosure defining a heating cavity for receiving therein a body to be heated, source means electrically coupled to said heating cavity for transmitting thereinto microwave electromagnetic energy to excite a predetermined primary electromagnetic field mode in said cavity at a first mode frequency, drive means including a rotatably driven grounded conductive shaft extending into said cavity with the longitudinal axis thereof disposed substantially parallel to the electric field component of said primary mode, a generally L-shaped conductive member disposed in said cavity and having two interconnected leg portions intersecting at an angle and lying in a common plane substantially normal to the axis of said shaft, said shaft being connected to said conductive member at the free end of one of the said leg portions thereof for effecting rotation thereof in a predetermined path about the axis of said shaft, said conductive member being responsive to continuous rotation thereof by said drive means for interaction with said primary mode electric field periodically to excite in said cavity a predetermined secondary electromagnetic field mode complementary to said primary mode and at a second mode frequency, and two tuning members mounted in said cavity adjacent to said predetermined path and arranged symmetrically with respect to the axis of said shaft for coupling said secondary mode and changing the frequency thereof toward said first mode frequency substantially without affecting the coupling of said primary electromagnetic field mode, whereby there is established within said cavity a substantially uniform time-averaged field distribution to facilitate uniform heating of the associated body.

Continuous tio fr or interaction with said primary mode electric field periodically to excite in said cavity two predetermined secondary electromagnetic field modes complementary to said primary mode, one of said secondary modes being at said second mode frequency and the other of said secondary pdss bs qaat aftesyensxhs ws n sa rstan ond mode frequencies. V w

6. The electronic heating apparatus set forth in claim 4, wherein said first mode frequency is approximately 920 MH,,, and said second mode frequency is approximately 960 MH 7. The electronic heating apparatus set forth in claim 4, wherein each of said tuning members has an effective electrical length approximately equal to one-fourth of the wavelength of the electromagnetic energy transv mitted into said cavity from said source means.

8. The electronic heating apparatus set forth in claim 4, wherein each of said tuning members is generally L- shaped and includes a first leg disposed substantially Perpendicular t aistshaftairt? s z9a2 ss.intsra1 with said first leg and disposed substantially normal thereto, said tuning members being respectfully disposed on opposite sides of said shaft and being equidistantly spaced therefrom. I

9. The electronic heating apparatus set forth in claim 4, wherein each of said tuning members is generally L- shaped and includes a first leg disposed substantially perpendicular to the axis of said shaft and a second leg integral with said first leg and disposed essentially normal thereto, said tuning members being respectively disposed on opposite sides of said shaft and equidistantly spaced therefrom with the longitudinal axes of said first legs being substantially collinear.

it). The electronic heating apparatus set forth in c aim ,tzrwhs emrsa d..cqndustivemembe sas s lly L-shaped including a pair of interconnected leg portions disposed in a common plane substantially normal to the axis of said shaft, each of said tuning members being generally L-shaped and including a first leg disposed substantially perpendicular to the axis of said shaft and asecond leg integral with said first leg and 10 disposed essentially normal thereto, said tuning members being respectively disposed on opposite sides of said shaft and equidistantly spaced therefrom with said first legs being disposed above the plane of said conductive member with the longitudinal axes thereof being substantially collinear.

ill. The electronic heating apparatus set forth in claim 4, wherein said conductive member is generally ,W.'$ P .QE .9Fl s arranged swastrlsddwithrssrsst to the axis of said shaft, each of said tuning members being generally L-shaped and including a first leg disposed substantially perpendicular to the axis of said shaft and a second leg integral with said first leg and disposed essentially normal thereto, said tuning members being respectively disposed on opposite sides of said shaft and equidistantly spaced therefrom with the longitudinal axes of said first legs being substantially colinear, said tuning members being respectively disposed on opposite sides of said shaft and equidistantly spaced therefrom with said first legs being disposed above the plane of said conductive member with the longitudinal axes thereof being substantially collinear.

112. Electronic heating apparatus comprising an enclosure defining a heating cavity for receiving therein a body to be heated, source means electrically coupled to said heating cavity for transmitting thereinto microwave electromagnetic energy to excite a predetermined primary electromagnetic field mode in said cavity at a first mode frequency, a grounded conductive member mounted in said cavityfor rotation about an axis disposed substantially parallel to the electric field component of said primary mode to excite in said cavity a predetermined secondary electromagnetic field mode complementary to said primary mode and at a second mode frequency, and tuning means mounted in said cavity for coupling said secondary electromagnetic field mode and changing the mode frequency thereof toward said first mode frequency substantially without affecting the coupling of said primary electromagnetic field mode, whereby there is established within said cavity a field distribution adapted to provide improved heating of the associated body.

=l= l l l 

1. Electronic heating apparatus comprising an enclosure including two opposed parallel walls and defining a heating cavity for receiving therein a body to be heated, an antenna disposed in said cavity adjacent to one of said opposed walls and having a longitudinal axis substantially perpendicular to said one wall, said antenna being adapted for coupling to an associated source of microwave electromagnetic energy for transmitting said energy into said cavity to excite therein a predetermined primary electromagnetic field mode at a first mode frequency, a grounded conductive member disposed in said cavity adjacent to the other of said opposed walls, drive means coupled to said conductive member for effecting rotation thereof about said axis of said antenna for exciting in said cavity a predetermined secondary electromagnetic field mode complementary to said primary mode and at a second mode frequency, and tuning means mounted in said cavity for coupling said secondary electromagnetic field mode and changing the mode frequency thereof toward said first mode frequency substantially without affecting the coupling of said primary electromagnetic field mode, whereby there is established within said cavity a field distribution adapted to provide improved heating of the associated body.
 2. The electronic heating apparatus set forth in claim 1, wherein said second mode frequency is higher than said first mode frequency, said tuning means effecting lowering of the frequency of said secondary mode to a range below said second mode frequency and including said first mode frequency.
 3. The electronic heating apparatus set forth in claim 1, wherein said first mode frequency is approximately 920 MHz, and said second mode frequency is approximately 960 MHz, said tuning means effecting reduction of the frequency of said secondary mode to a range of frequencies between 890 and 940 MHz.
 4. Electronic heating apparatus comprising an enclosure defining a heating cavity for receiving therein a body to be heated, source means electrically coupled to said heating cavity for transmitting thereinto microwave electromagnetic energy to excite a predetermined primary electromagnetic field mode in said cavity at a first mode frequency, drive means including a rotatably driven grounded conductive shaft extending into said cavity with the longitudinal axis thereof disposed substantially parallel to the electric field component of said primary mode, a generally L-shaped conductive member disposed in said cavity and having two interconnected leg portions intersecting at an angle and lying in a common plane substantially normal to the axis of said shaft, said shaft being connected to said conductive member at the free end of one of the said leg portions thereof for effecting rotation thereof in a predetermined path about the axis of said shaft, said conductive member being responsive to continuous rotation thereof by said drive means for interaction with said primary mode electric field periodically to excite in said cavity a predetermined secondary electromagnetic field mode complementary to said primary mode and at a second mode frequency, and two tuning members mounted in said cavity adjacent to said predetermined path and arranged symmetrically with respect to the axis of said shaft for coupling said secondary mode and changing the frequency thereof toward said first mode frequency substantially without affecting the coupling of said primary electromagnetic field mode, whereby there is established within said cavity a substantially uniform time-averaged field distribution to facilitate uniform heating of the associated body.
 5. The electronic heating apparatus set forth in claim 4, wherein said conductive member is responsive to continuous rotation thereof for interaction with said primary mode electric field periodically to excite in said cavity two predetermined secondary electromagnetic field modes complementary to said primary mode, one of said secondary modes being at said second mode frequency and the other of said secondary modes being at a frequency between said first and second mode frequencies.
 6. The electronic heating apparatus set forth in claim 4, wherein said first mode frequency is approximately 920 MHz, and said second mode frequency is approximately 960 MHz.
 7. The electronic heating apparatus set forth in claim 4, wherein each of said tuning members has an effective electrical length approximately equal to one-fourth of the wavelength of the electromagnetic energy transmitted into said cavity from said source means.
 8. The electronic heating apparatus set forth in claim 4, wherein each of said tuning members is generally L-shaped and includes a first leg disposed substantially perpendicular to said shaft and a second leg integral with said first leg and disposed substantially normal thereto, said tuning members being respectfully disposed on opposite sides of said shaft and being equidistantly spaced therefrom.
 9. The electronic heating apparatus set forth in claim 4, wherein each of said tuning members is generally L-shaped and includes a first leg disposed substantially perpendicular to the axis of said shaft and a second leg integral with said first leg and disposed essentially normal thereto, said tuning members being respectively disposed on opposite sides of said shaft and equidistantly spaced therefrom with the longitudinal axes of said first legs being substantially collinear.
 10. The electronic heating apparatus set forth in claim 4, wherein said conductive member is generally L-shaped including a pair of interconnected leg portions disposed in a common plane substantially normal to the axis of said shaft, each of said tuning members being generally L-shaped and including a first leg disposed substantially perpendicular to the axis of said shaft and a second leg integral with said first leg and disposed essentially normal thereto, said tuning members being respectively disposed on opposite sides of said shaft and equidistantly spaced therefrom with said first legs being disposed above the plane of said conductive membEr with the longitudinal axes thereof being substantially collinear.
 11. The electronic heating apparatus set forth in claim 4, wherein said conductive member is generally W-shaped and is arranged symmetrically with respect to the axis of said shaft, each of said tuning members being generally L-shaped and including a first leg disposed substantially perpendicular to the axis of said shaft and a second leg integral with said first leg and disposed essentially normal thereto, said tuning members being respectively disposed on opposite sides of said shaft and equidistantly spaced therefrom with the longitudinal axes of said first legs being substantially colinear, said tuning members being respectively disposed on opposite sides of said shaft and equidistantly spaced therefrom with said first legs being disposed above the plane of said conductive member with the longitudinal axes thereof being substantially collinear.
 12. Electronic heating apparatus comprising an enclosure defining a heating cavity for receiving therein a body to be heated, source means electrically coupled to said heating cavity for transmitting thereinto microwave electromagnetic energy to excite a predetermined primary electromagnetic field mode in said cavity at a first mode frequency, a grounded conductive member mounted in said cavity for rotation about an axis disposed substantially parallel to the electric field component of said primary mode to excite in said cavity a predetermined secondary electromagnetic field mode complementary to said primary mode and at a second mode frequency, and tuning means mounted in said cavity for coupling said secondary electromagnetic field mode and changing the mode frequency thereof toward said first mode frequency substantially without affecting the coupling of said primary electromagnetic field mode, whereby there is established within said cavity a field distribution adapted to provide improved heating of the associated body. 